Study On Structure And Capability Of Mo-MoSi₂ Functionally Gradient Material

In order to exert the outstanding properties of molybdenum and molybdenum disilicide, Mo-MoSi₂ functionally gradient material is prepared by electrochemical method in molten salt system. It has important academic meaning and applied value to study the preparation technique and capability of Mo-MoSi₂ functionally gradient material. A detailed study, which includes the chemical reaction in the Mo-Si system, the preparation of Mo-MoSi₂ functionally gradient material in NaCl-KCl-NaF-SiO₂ molten salt system by molten salts electrodeposition ihrigizing, and the microstructures of functionally gradient material and its performances, is made in this dissertation.From the aspect of thermodynamics, the chemistry reactions and condition are confirmed, influences of Mo,Si content on Substance Structures in different Functionally Gradient Layers is calculated. The results go as following. MoSi₂ is created easily in 1073-1168K; the changing rule along the Mo-base along with the increase of Si content goes as Mo→Mo₅Si₃+Mo₃Si+Mo→Mo₃Si+Mo₅Si₃+MoSi₂→Mo₅Si₃+MoSi₂→MoSi₂+Si→Si.The metallurgical structure of Mo-MoSi₂ functionally gradient material is studied by single factor examination. The corrosive time which is 30 seconds and corrosive agent which is made by 12ml niteic acid,12ml hydrofluoric acid and 18ml glycerol are confirmed.Steady columnar crystal is the mainly style in the sedimentary deposit under kinds of technological conditions. And the electrodeposition effect is the best in the condition of D>0,t₁/t₂=6/4,120minutes,800～850℃and1000A·m^-2.The texture of Mo-MoSi₂ functionally gradient material is studied by part extremal graph.Seriate columnar crystals are formed by the effect of electric field. And the form and textured degree in sedimentary deposit are influenced by the electric current density and temperature.The bend capability is measured by three points bending. And the surface hardness is measured by Vickers microhardness. The results are as following. The bend strength of Mo-MoSi₂ functionally gradient material is mainly provided by the molybdenum base, and it's valueable is more two times than the hardness of molybdenum base before elecrodeposition. The best elecrodeposition condition is pulse square wave, 850℃, 1000A·m^-2 and t₁/t₂=2. The surface hardness of Mo-MoSi₂ gradient material is reduced after heat treatment. The bond strength of Mo-MoSi₂ functionally gradient material between molybdenum base and sedimentary deposit is measured by bending, indentation, file, scarification and thermal vibration experiment. The results indicate that the molybdenum base and sedimentary deposit is hanged together close by diffusion bonding and epitaxial growth bonding. It is provided with excellent bond strength.The low and high temperature inoxidizable performnaces of Mo-MoSi₂ functionally gradient material are studied by oxidation weight growth. And the oxidation mechanism of Mo-MoSi₂ functionally gradient material is analized by kinds of test method emphatically.It is find that the Mo-MoSi₂ functionally gradient material is provided with excellent oxidation resistant capability both at low and high temperature. The destructive volatilization of molybdenum at 800℃is not happened, and the"pulverization pestilence"of MoSi₂ is not happened too, so the Mo-MoSi₂ functionally gradient material can be used in the suitable condition.